Alexa Chung, a Londoner indeed, does the light coat nicely -- I find that her coats usually add to her outfits in kind of a fun and unexpected way. All seeming, of course, as if no effort whatesoever was put in to pulling her outfit together. Sure.
I've done some searching and found my Etsy favorites:
A wide-weave swing coat from allencompanyinc on Etsy.
The classic Burberry trench (vintage) at katyagray at Etsy.
60s Navy Coat at Londablanca at Etsy.
Pink Velveteen dress, also at Londablanca at Etsy
And, finally, a classic dream trench, by Tsumori Chisato at La Garconne: